Is the Sigma 70-200mm F2.8 DG DN OS Sports Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 100mm f/2.8 test image. Observe the contrast and resolution of these results.
Is the Sigma 70-200mm F2.8 DG DN OS Sports Lens set to 100mm f/2.8 sharper than the Sony FE 70-200mm F2.8 GM OSS II Lens set to 280mm f/4.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.